Material handling systems for assembly-line fabrication are generally designed to facilitate efficient and rapid fabrication of an assembly from a plurality of parts or sub-assemblies. One area particularly suited to such material handling systems is automotive manufacturing. For example, material handling systems may be used for the assembly of a vehicle's sheet metal body, power train, chassis sub-assemblies, or trim. Material handling systems may also be used in painting operations, welding, bonding, or other general assembly operations.
Generally a carrier, a structure for accumulating the various parts and sub-assemblies that will eventually be joined to a vehicle body, travels through a plurality of stations. At each station, components may be added and/or joining operations may be performed (e.g., resistance welding, adhesive bonding, stud welding, etc.) by a plurality of robots or tradesman. Individual components or sub-assemblies may be provided to the various stations by a magazine, which presents the parts to the robots or tradesmen in a consistent orientation and at sufficient frequency to match the pace of an assembly line. Either at discrete stations, or in conjunction with other tasks, a plurality of geometric orientation tools (“geo-tools”) may be used to manipulate the parts into precise alignment with various reference points prior to being permanently joined.
Often, the carrier may be conveyed by a generic transfer frame. The transfer frame may be moved from station to station by a variety of different transfer systems, such as an overhead track system, for example, and may be raised and lowered with respect to the stations.
There are several disadvantages traditional conveyance systems. For example, the transfer frame and carriers produce a bulky combined assembly. At the end of the assembly line, each of the transfer frames and carrier assemblies must be returned to the beginning of the line. This often involves dedicating a return loop, typically located above the assembly line, for the purpose of returning the empty carriers and frames. Unfortunately, this return loop generally bisects an upper catwalk and, therefore, prohibits maintenance personnel on one side from being able to safely pass to the other side of the catwalk. This greatly hinders troubleshooting and access to equipment cabinets and overhand routed utilities.
Additionally, each of the frames and carriers may be communally tied to an overhead conveyer. Accordingly, carriers and frames at one station cannot be moved independently with respect to carriers and frames at other stations. This results in a lack of flexibility, and carriers are unable to rapidly pass through unnecessary stations. Moreover, carriers must be moved through the various stations at a constant movement and delay pattern. A carrier and corresponding parts undergoing processing at one station, even when processing is completed, cannot move until all of the other stations have completed their respective tasks. Limit switches, slow switches, and stop switches control the overhead conveyer as one collective unit.
Therefore, an improved non-overhead conveyance system with improved flexibility is needed.